4′-GL is known as the main component of galacto-oligosaccharide that can promote proliferation of enteric Bifidobacteria. 4′-GL is also used as an index of galacto-oligosaccharide analysis.
Industrial production of 4′-GL-containing galacto-oligosaccharides utilizes a transfer reaction by β-galactosidase, using lactose as the feedstock. However, the purity of the galacto-oligosaccharide itself is typically low when purification step and the like are not performed.
As a technique that improves purity through purification of oligosaccharide, PTL 1 discloses a glucosamino oligosaccharide purification method in which a polymer prepared by introducing a carboxylmethyl group to a polymer having a hydroxyl group is used as a chromatography filler. However, there is no report of a method that is intended to improve the purity of components of galacto-oligosaccharide, particularly 4′-GL, through purification of galacto-oligosaccharide. Even compositions available as a reference standard of 4′-GL are not sufficient in purity.